653 
MR. H. B. DIXON OX CONDITIONS OF CHEMICAL CHANGE 
and steam on the other, which can take place at the high temperature produced by 
the combustion.” 
This view of the final result of the reaction, which appears to me to be substantially 
correct, seems difficult to reconcile with Horstmann’s previous conclusions as to the 
function of nitrogen and carbonic acid in the explosive mixture. For if the final result 
depend^ upon an equilibrium being established between the reduction of the carbonic 
acid by the hydrogen and the oxidation of the carbonic oxide by the steam, how is it 
possible for nitrogen to take the place, and play the part, of an equal quantity of 
hydrogen or carbonic oxide ? 
The following is Horstmann’s conclusions with regard to the variation of the 
coefficient with the percentage of oxygen taken :— 
“ The coefficient is probably dependent alone upon the temperature. The influence of 
the temperature is of a complicated kind. A portion of the carbonic acid and steam is 
dissociated at the temperature reached. As the temperature sinks, the equilibrium 
alters with it. The composition of the mixture corresponds therefore to an equilibrium 
for some unknown middle value between the temperature of combustion, which varies 
with the composition of the mixture, and the lower limit of temperature, at which 
the mutual action of the gases is just possible. This lower limit of temperature is 
the same with all mixtures.” 
From his latest experiments (not yet published) Horstmann concludes that the 
values of the coefficient, which by the earlier experiments fell between 4 and 7, may 
be much lower at low temperatures : for the lowest temperatures even less than 1. 
This shows that, contrary to what is found at high temperatures, the affinity of 
oxygen for carbonic oxide at low temperatures is greater than for hydrogen ; a result 
which confirms the statement of E. von Meyer that in the slow combustion effected 
by platinum at ordinary temperatures more carbonic oxide is burnt than hydrogen. 
I shall show later that the proportionality discovered by Horstmann between the 
ratios of the unburnt gases and the products of combustion is a fact independent of 
the percentage of combustible gases burnt, and dependent only on the conditions (1) 
that a sufficiently high temperature should be reached in the explosion, (2) that none 
of the reacting molecules should be withdrawn from the sphere of action during the 
chemical change, and (3) that no indifferent gas should be present. 
Experiments with dry gases above the critical pressure. 
To test the accuracy of Horstmann’s conclusions, the following experiments were 
made with dry gases exploded at high pressures. A dry mixture of carbonic oxide 
and oxygen and a dry mixture of hydrogen and oxygen, each containing 12'4 per 
cent, of oxygen, were made. Varying proportions of each of these mixtures were 
brought together in the eudiometer and exploded under 1000 millims. pressure. In 
these experiments the ratio of carbonic oxide and hydrogen is varied ; about 12'4 
per cent, of oxygen is employed in each case; and the pressure is such that no 
increase of pressure or variation in the length of column makes any difference in 
